Dynamic leak control for system with working fluid

ABSTRACT

An organic rankine cycle system includes a sensor for sensing a condition indicative of pressure within the system and a control which responsively provides heat to said system when the pressure within the system is sensed to be at a predetermined threshold, near ambient pressure, during periods in which the system is shut down or preparing to operate. Provision is also made to remove the heat from the system when the pressure therein rises to a predetermined higher pressure threshold.

TECHNICAL FIELD

This disclosure relates generally to closed loop systems with apressurized working fluid, and, more particularly, to a method andapparatus for preventing the migration of contaminant gases into thesystem during shut down.

BACKGROUND OF THE DISCLOSURE

Closed loop systems often contain a working fluid with propertiesspecific to the successful or efficient operation of the equipment. Theworking fluid properties may be degraded by the addition of foreign,particles. Closed, loop systems generally operate at elevated pressuresrelative to ambient pressure. This ensures that leaks propagate out ofthe system during operation. During system shutdown, this scenario maybe reversed with the closed loop system pressure at or below ambientpressure. As a result, molecules such as oxygen and nitrogen may migrateinto the system. These pollute the working fluid and negatively, impactthe subsequent operation and efficiency of the system. Currently,related systems require a purge device that extracts the systempollutants from the working fluid.

One such closed loop system is that of an organic rankine cycle systemwhich includes in serial flow relationship, an evaporator or boiler, aturbine, a condenser and a pump. Such a system is shown and described inU.S. Pat. No. 7,174,716, assigned to the predecessor of the assignee ofthe present invention.

DISCLOSURE

In accordance with one aspect of the disclosure, a heat source isoperatively connected to the evaporator and has a control which isresponsive to a condition sensor for maintaining the pressure in thesystem above a predetermined threshold.

In accordance with another aspect of the disclosure, a process ofpreventing migration of impurities into a closed loop system during shutdown includes the steps of sensing the pressure in the system andresponsively operating a heat source so as to maintain the pressure inthe system above a predetermined threshold.

In the drawings as hereinafter described, a preferred embodiment isdepicted; however, various other modifications and alternateconstructions can be made thereto without departing from the spirit andscope of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an organic-rankine cycle systemwith the present invention incorporated therein.

FIG. 2, is a graphical illustration of the manner in which the pressureis controlled in accordance with the present invention.

FIG. 3 is a schematic illustration of an organic rankine cycle systemwith a modified embodiment of the present invention incorporatedtherein.

DETAILED DESCRIPTION OF THE DISCLOSURE

Shown in FIG. 1 is an organic ranking cycle system which includes, inserial working-fluid-flow relationship, an evaporator 11, a turbine 12,a condenser 13 and a pump 14. The working fluid flowing therethrough canbe of any suitable refrigerant such as refrigerant R-245fa, R134,pentane, for example.

The energy which is provided to drive the system is from of a primaryheat source 16 by way of a closed loop which connects to the evaporator11 by way of lines 17 and 18. A valve 20 is provided to turn this flowon or off and may be located either upstream or downstream from the heatexchanger 16. The primary heat source 16 may be of various types suchas, for example a geothermal source, wherein naturally occurring hotfluids are available below the surface of the earth. The temperatures ofsuch geothermal sources are generally greater than 150-F, sufficient tooperate most working fluids well above atmospheric pressure.

After the working fluid is heated in the evaporator 11, it passes as ahigh temperature, high pressure vapor to the turbine 12 where the energyis converted to motive power. The turbine 12 is drivingly attached to agenerator 19 for generating electrical power that then passes to thegrid 21 for further distribution.

After passing to the turbine 12, the working fluid, which is now a vaporwhich is at a reduced temperature and pressure vapor, passes to thecondenser 13, which is fluidly connected to a cooling water source 22 bylines 23 and 24. The condenser 13 functions to condense the workingfluid vapor into a liquid, which then flows along line 26 to the pump14, which then pumps the liquid working fluid back to the evaporator 11by way of line 27.

During normal operation of the above described organic rankine cyclesystem, because of the energy added by the primary heat source 16, theworking fluid always remains at a pressure substantially greater thanambient pressure. However, during selected periods of time, such asduring oil warm up or when the system is shut down, such as, forexample, during periods of maintenance and/or repair, then the workingfluid therein slowly cools and eventually may reach ambient temperature.At this point, because of the thermodynamic, properties of the workingfluid that relates temperature and pressure of a saturated system, thepressure within the system will tend to further decrease to a levelbelow ambient pressure. This low pressure condition will then allow themigration of contaminating gases, such as oxygen and/or nitrogen, tomigrate into the system from the atmosphere. The present disclosure isintended to prevent such a migration from occurring.

In one form of the disclosure, a sensor 27 is provided to sense acondition indicative of pressure in the system, such as the temperatureor pressure within the evaporator 11, and to send a responsive signalalong line 28 to, a control 29. Control 29 is connected by a line 31 toa valve 32 with the valve 32 then being operated by the control 29 inresponse to the sensed temperature/pressure in such a manner as tomaintain the temperature/pressure in the evaporator 11 at a level whichwill remain above the ambient pressure/temperature and therefore preventthe migration of unwanted gases into the system during periods of shutdown.

Referring now to FIG. 2, the pressure within the system is shown as afunction of time in which the system is operating normally and then isshutdown, with the present invention then operating to prevent migrationof the gases into the system.

As will be seen, at time t₁ the system is operating normally such thatthe pressure is at P₁. Further, at time t₂, the system is shut down andthe pressure begins to decline, and at time t₃, reaches a thresholdlevel of P₃, which is lightly above the anticipated ambient pressure P₄for the environment of the warming system. When this threshold pressureis reached, the sensor 27 signals the control 29 which then opens thevalve 32 to provide heat to the evaporator 11 to thereby cause thepressure in the system to be gradually increased.

At time t₄, a second threshold of pressure equals P₂ and the control 20then responsively moves, the valve 32 to a fully closed or at least apartially closed position. The pressure of the system is then graduallyreduced such that at time t₅ it again reaches the lower threshold of P₃wherein the control 29 again opens the valve 32 to add heat to thesystem. At time t₆, the control again moves the valve 32 to amore-closed position. This cycle is repeated so as to maintain thesystem at a pressure above that of ambient so that migration of gasesinto the system is prevented during shut down. When normal operationresumes, the control 29 remains in an inactive condition until called onto be activated by the sensor 27 when, for example, the system is againshutdown.

An alternative embodiment is shown in FIG. 3 wherein a sensor 33 sensesthe pressure within the condenser 13 rather than within the evaporator11. In this regard, it is recognized that during the period followingshut down, the pressures in the evaporator 11 and in the condenser 13tend toward equalization since they are only separated on one side bythe pump 14 which provides nearly complete restriction between the two,and on the other side by the turbine 12 which provides only a partialrestriction between the two tanks.

Another alternative is to use a supplementary heat source 36 rather thanthe primary heat source 16 during periods of shut down. Such asupplementary heat source might be steam or hot water from a sourceother than the primary heat source 16, or it may be by way of anelectrical resistance heater. Similar to the FIG. 1 embodiment, thesensor 33 sends a signal to the control 34 which then responsivelyoperates the supplementary heat source 36 to maintain the pressure inthe system above the ambient pressure during shut down.

As another alternative, to ensure that the two tanks i.e. the evaporator11 and the condenser 13, are maintained at substantially the samepressure during pressure shut down, the two may be selectively fluidlyinterconnected by way of a line 37 and valve 38, with the valve 38 beingcontrolled by way of the control 34.

While the present invention has been particularly shown and describedwith reference to preferred and modified embodiments as illustrated inthe drawings, it will be understood by one skilled in the art thatvarious changes in detail may be made thereto without departing from thespirit and scope of the disclosure as defined by the claims.

1. A method of preventing migration of gases into a closed loop organicrankine cycle system during selected periods of time comprising thesteps of: establishing a threshold pressure to be maintained in thesystem in order to prevent migration of gases thereinto when the systemis in a shut down condition; providing a sensor for sensing acharacteristic indicative of the pressure within the system during suchperiods; and wherein said threshold pressure is sensed, providing heatto said system to cause the pressure therein to rise above the thresholdpressure so as to prevent migration of gases into the system.
 2. Amethod as set forth in claim 1 wherein said sensor is a pressure sensor.3. A method as set forth in claim 1 wherein the condition sensed is inthe evaporator of the system.
 4. A method as set forth in claim 1wherein said established threshold is above the anticipated external orambient pressure relative to the system.
 5. A method as set forth inclaim 4 wherein said threshold pressure is slightly above theanticipated external or ambient pressure relative to the system.
 6. Amethod as set forth in claim 1 wherein the step of providing heat is byway of a primary heat source, which is a heat source used during normaloperation of the organic rankine cycle system.
 7. A method as set forthin claim 1 wherein the step of providing heat to the system is by way ofa secondary heat source, which is separate from the heat source used inthe normal operation of the organic rankine cycle system.
 8. A method asset forth in claim 1 and including the further steps of: establishing asecond, higher threshold pressure; and when the sensed pressure in thesystem reaches said second higher threshold, removing heat from thesystem.
 9. A method as set forth in claim 1 wherein the condition sensedis in the condenser.
 10. A method as set forth in claim 1 and includingthe further step of fluidly interconnecting an evaporator and acondenser of the system when said threshold pressure is sensed.
 11. Anapparatus for preventing migration of gases into a closed loop organicrankine cycle system during periods of shut down, comprising: a sensorfor sensing a condition indicative of pressure within the system duringperiod of shut down; a heater for selectively providing heat to saidsystem during periods of shut down; and a control responsive to saidsensor to cause said heater to provide heat to said system when thesensed pressure reaches a predetermined lower threshold level.
 12. Anapparatus as set forth in claim 11 wherein said sensor is a pressuresensor.
 13. An apparatus as set forth in claim 11 wherein said sensor isconnected to sense the condition within the evaporator.
 14. An apparatusas set forth in claim 11 wherein said predetermined lower threshold is apressure above the anticipated ambient pressure of the system.
 15. Anapparatus as set forth in claim 4 wherein said threshold is slightlyabove the anticipated ambient pressure of the system.
 16. An apparatusas set forth in claim 11 wherein said heat source comprises a primaryheat source that is used during normal operation of the organic rankinecycle system.
 17. An apparatus as set forth in claim 11 wherein saidheat source is a secondary heat source which is different from a primaryheat source which is used for normal operation of the organic rankinecycle system.
 18. An apparatus as set forth in claim 11 wherein saidcontrol is responsive to a second threshold higher than said firstthreshold, for removing the heat from said system.
 19. An apparatus asset forth in claim 11 wherein said condition sensed is in the condenserof the system.
 20. An apparatus as set forth in claim 11 and including afluid connection between a condenser and an evaporator of the organicrankine cycle system made response to the control when said firstthreshold is sensed.